The Irish province claimed their second successive RaboDirect PRO12 title at the RDS with a 34-12 defeat of Glasgow Warriors.
But disaster struck for Leinster after nine minutes when O'Driscoll, playing in his last professional match, was forced off with a calf injury; but in his place came Madigan and Leinster stormed to victory.
Two penalties from Finn Russell gave Glasgow and early lead but Zane Kirchner's try on 17 minutes got Leinster off the mark.
A try for Shane Jennings before the break gave Leinster the lead but another Russell penalty kept Glasgow in touch.
However, Leinster eventually sealed the win and O'Connor believes it would be foolish to overlook the impact of Madigan.
"He (Madigan) is a class footballer. He has played a hell of a lot of rugby at 12. He gave us an extra set of hands there, which created a lot of opportunities and asked questions of the Glasgow defence," said O'Connor.
"There has never been a doubt in how good a footballer Ian Madigan is from this side of the table.
"The last two performances of the season, he has come on early and changed the game for us. That says to me that he is in a pretty good frame of mind mentally.
"The challenges that he has had - he is running the game and being the focal point of the opposition - that takes time, and he will develop the more and more he does that.
"I thought he and Jimmy (Gopperth) tonight worked in tandem brilliantly, and it was a very pleasing result for Ian personally."
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